List of Lessons
Lesson 1-3 NORMAL CELL MATURATION
In the course of blood cell maturation, certain specific features are developed (see figure 1-4). Each of the component parts of the cell undergoes a transformation during maturation. The immature cell or blast cell contains a large nucleus, a small amount of cytoplasm, and no granules. As the cell ages, the cytoplasm becomes less basophilic and nuclear chromatin becomes heavier (darker stain). Reduction in size and loss of nucleoli occurs as the cell becomes older. The three types of granulation (neutrophilic, basophilic, and eosinophilic) become more specific and smaller as the cell ages. Maturation, in general, involves:
- (1) cytoplasmic differentiation
- (2) nuclear maturation,
- (3) reduction in cell size
The basophilia of a blast cell is proportional to the ribonucleic acid (RNA) content. As the cell matures, the RNA content decreases and the cell becomes a paler blue. In the myeloid cells, a specific type of granulation occurs. When granules appear they are pinkish-red and few in number. The granules increase in number and differentiate into three types upon maturation. As the cell matures, it develops an affinity for the acid or basic portion of the stain (Wright’s stain). Basophilic granules stain blue-black, eosinophilic granules stain red-orange, and neutrophilic granules stain pinkish-purple. Lymphocytes are usually devoid of cytoplasmic granulation but they can possess non-specific azurophilic (dark-purple) granules, usually characteristic of monocytes and plasmocytes. Upon maturation, the erythrocyte develops a light orange respiratory pigment called hemoglobin.
The nucleus of the young cell is large, round, and occupies most of the cell. As the cell matures, the size of the nucleus decreases. Nuclei of early or primitive cells usually have one or more nucleoli. The latter are small, round, homogeneous areas that usually stain light blue with a darker boundary. In appearance nucleoli are somewhat like craters in the nucleus. They are surrounded by strands of chromatin.These nucleoli, plus a delicate reticular network of chromatin, are the principle indicators of blood cell immaturity. As the cells mature, the nucleus gradually becomes smaller, stains darker, and chromatin meshwork become “coarse” with the strands of chromatin less fine and lacelike. In the course of cell development, the nucleus changes its shape, particularly in the granulocytic series, where it becomes indented, lobulated, segmented, or fragmented. As maturation or development progresses, the nucleus, if still intact, becomes small, compact, usually dark and structureless, and can completely disappear. The loss or shrinking of the nucleus is accompanied by a decrease in cell size.
Figure 1-4. Development of blood cells.